The invention relates to rubber compounds based on rubber particles and phosphoryl polysulfides, as well as to vulcanizates or shaped articles prepared therefrom. The addition of phosphoryl polysulfides improves the strengthening effect of the rubber particles, in particular, the product S300xc3x97D of the modulus at 300% elongation (S300) and the elongation at break (D), without lowering the resilience of the vulcanizates prepared therefrom.
Fillers are used to improve the mechanical properties of vulcanized rubber articles. Those with the greatest industrial importance are carbon blacks and silicas. The use of fillers provides higher vulcanizate hardnesses, higher moduli and higher strengths than in the case of the corresponding unfilled vulcanizates. According to the strengthening effect of the fillers, distinction is made between inactive, active and highly active fillers. Especially in the case of inorganic fillers, their high density (carbon black: 1.8 g/cm3; silica: 2.1 g/cm3) leads to a compromise in terms of the weight of the rubber article prepared therefrom.
The use of microgels as filler is described in the following patent applications, or patents: EP-A 405 216, DE-A 4 220 563, GB-PS 1 078 400, DE-A 197 01 489, EP-A 432 405 and EP-A 432 417. The use of CR, BR and NR microgels in compounds with rubbers that contain double bonds is claimed in patent (applications) EP-A 405 216, DE-A 4 220 563 and in GB-PS 1 078 400. The resilience of the filled vulcanizates, especially at 70xc2x0 C., is advantageous. The strengthening effect of the microgels (modulus) is not sufficient for industrial use. This is demonstrated, in particular, by the fact that large amounts of gel need to be used in order to obtain industrially suitable modulus ranges. These large amounts of gel lead to overfilling of the compounds, so that the elongations at break are reduced. There is, therefore, an industrial need, in the case of gel-filled vulcanizates, to find ways of increasing the product of the modulus at 300% elongation (S300) and the elongation at break (D), without simultaneously compromising the resilience at 70xc2x0 C.
The use of phosphoryl polysulfides in rubber compounds is disclosed by the product data sheet from Rhein Chemie Rheinau GmbH Rhenocure(copyright) SDT/S xe2x80x9cKonfektionierte Kautschukchemikalien und Additivexe2x80x9d [manufactured rubber chemicals and additives] 09.99 edition. The purpose of the phosphoryl polysulfides is to provide non-discoloring sulfur donors for the vulcanization of natural and synthetic rubber. Phosphoryl polysulfides act as sulfur donors which lead to monosulfide and disulfide crosslinking bridges with good reversion stability during vulcanization and in vulcanized articles. The product data sheet does not, however, teach the use of phosphoryl polysulfides to improve the strengthening effect of gel-filled vulcanizates.
It has now been found that, by adding phosphoryl polysulfides to rubber compounds which contain rubber gels, both the modulus at 300% elongation and the product of S300 and the elongation at break (S300xc3x97D) are improved without lowering the resilience at 70xc2x0 C.